Another Yanmar Question

[Don]

After motoring for a couple of hours the engine loses RPM's all on it's own. I throttle right back and run at lower RPM and then it seems to be fine for a while.
I replaced the air filter which was really bad, seemed almost oil soaked but have not had a long motor run to confirm that was a fix.
Could it possible be the fuel filters as well or would they just stop - they were changed out last year and not that many hours on the engine.
Any insight appreciated,
Thanks Don

 

[Larry]

Filters

Sounds like the fuel filters to me. Had the same problem, changed the one on the yanmar, no help. I found a second filter in the lazerett.


Larry

 

[RichH]

Several causes

1. Fuel starvation - obstructed dip tube screen in tank; restricted fuel tank vent; choked filters; leak in compression fitting; pin hole in lift pump diaphragm or faulty check valve in pump.
2. accumulation of 'coke' or impacted soot in injection nozzle - high back pressure.
3. that air filter on the engine ..... isnt .its actually a silencer and will only prevent the aspiration of rocks sticks, feathers and an occasional small dog.

 

[chesapeakesailor]

Definitely check your exhaust elbow

Could be soot in your cast iron exhaust elbow caused by excessive slag that shouldn't be there or dirty fuel injectors causing carbon build up. Either way the back pressure will likely put carbon particles in your lubricant turning it to grinding paste. I know because I just had to rebuild my 3.5 year old engine (Yanmar 3YM30) for $7.5K becuause I didn't know any better. Still need to call Yanmar and ask them how it's possible...

 

[Rob]

Fuel Level

I find this happens when I get down to about a 1/4 of a tank in rough water which is caused by the fuel sloshing around the tank away from the fuel pickup.

How much fuel did you have in the tank and did you hit a wake just before the RPMs dropped?

 

[Don]

Thanks for the input

Replaced the exhused elbow 2 years ago - still good water flow and no apparent overheating so I will eliminate that.
Will replace both fuel filters.
Will change oil and filter just as a prcation.
Tank was over 1/2 full so I think it was getting fuel - also calm seas.
Not sure about the screen on the pick-up but will take a look and see.
Injectors are beyond my level of expertise so if all else fails I will have to go to a Yanmaar dealer.